FB25 Engine Review: Problems, Specs and Reliability

Disclosure: we may earn a small commission from the companies mentioned in this post via affiliate links to products. This doesn't make any additional cost to you. All products are selected independently.

FB25 is a new-generation engine by Subaru brand, first produced in 2010. It is a 2.5L non-turbo boxer 4-cylinder motor, meant to substitute EJ25 in Subaru Legacy and Forester.

Being a more powerful modification of FB20, this motor features a great number of new technologies and innovations. It has an aluminum cylinder block and identical stroke, but 94 bore cast iron sleeves contribute to greater displacement. Cylinder walls are 3.5 mm thick. To decrease friction inside the block and lessen the compression index to 10.0:1, Subaru utilized restyled pistons.

FB motors keep aluminum heads (DOHC with 4 valves per cylinder), containing cylinder head and camshaft carrier, which decreases thickness and mass of metal. Lifters are replaced by roller rocker arms. Intake and exhaust camshafts feature AVCS, a variable valve timing system. After equipping cylinder heads with fuel injectors, engine became more powerful though the injection system is rather intricate.

To achieve higher airflow, Subaru restyled intake and exhaust valves and ports. Every FB25 motor is equipped with maintenance-free timing chains. Changes in exhaust system concerned fresh manifolds and diameters of tubes for more efficiency and catalytic converter warming-up improvement.

In 2014, some minor changes were made. Cylinder walls became thinner (3.2 mm) and fresh pistons were utilized to reach a higher compression index of 10.3:1. Heads gained restyled intake ports and other intake valves of 36 mm. Besides, the intake manifold and exhaust system were subjected to updates.

In comparison with EJ25, FB25 is more responsive at low speeds. Having an identical output, it achieves lower rpm and higher torque at lower rpm. Moreover, it consumes less fuel. As a result, FB25 turns out to have more benefits.

FB25 Specs

Manufacturer Gunma Oizumi Plant
Also called Subaru FB25
Production 2010-present
Cylinder block alloy Aluminum
Configuration Flat-4
Valvetrain DOHC
4 valves per cylinder
Piston stroke, mm (inch) 90 (3.54)
Cylinder bore, mm (inch) 94 (3.70)
Compression ratio 10.0
10.3 (2014+)
Displacement 2498 cc (152.4 cu in)
Power output 127 kW (172 HP) at 5,800 rpm
129 kW (175 HP) at 5,800 rpm
Torque output 236 Nm (174 lb·ft) at 4,100 rpm
235 Nm (173 lb·ft) at 4,000 rpm
Redline 6,000
HP per liter 68.9
Fuel type Gasoline
Weight, kg (lbs)
Fuel consumption, L/100 km (mpg)
Subaru Forester 2.5
10.9 (21)
6.8 (34)
8.3 (28)
Turbocharger  Naturally aspirated
Oil consumption, L/1000 km
(qt. per miles)
up to 1.0
(1 qt. per 600 miles)
Recommended engine oil 0W-20
Engine oil capacity, L (qt.) 4.8 (5.1)
Oil change interval, km (miles) 5,000-10,000
Normal engine operating temperature, °C (F)
Engine lifespan, km (miles)
-Official information

300,000+ (180,000)
Tuning, HP
-Max HP
-No life span loss


  • 2011+ North American Subaru Forester
  • 2013+ North American Subaru Legacy

Is Subaru FB25 an interference motor?

Yes, FB25 is an interference motor. All Subaru engines since  2010 are interference.

FB25 Engine Problems and Reliability


The FB25 has no issues with high oil consumption instead of the FB20. The lifespan of the maintenance-free timing chains and associated systems (slider, tensioner, etc.) is designed to be about the same as the useful lifespan of the engine itself.

The engine is good and reliable, the lifespan is about 200,000 miles.

Last update on 2021-10-16 / Affiliate links / Images from Amazon Product Advertising API

Dan Hoffman

Dan is a co-founder of Engineswork. He knows everything about internal combustion engines. Ask your questions in comments down below this article - he will be glad to help you anytime.

Recent Posts